Train Low. Race High.

Even if you live at sea level you can run a mountain trail race

Photo by Rob O'Dea

When runners cross the finish line of the Leadville Trail 100, a broad-shouldered beast of a race between 9200 and 12,600 feet in the Colorado Rockies, they receive a medal, hug from Race Director Merilee O'Neal and an escort to the medical tent, just 20 yards away. Inside the army-green canvas tent, it feels like a M.A.S.H. unit. Filthy runners are supine, many wearing oxygen masks and draped with wool blankets. Chunky coughs and soft moans reverberate.

Medical personnel take runners' oxygen-level readings, connecting a small clip to a finger. The normal level here, on America's highest Main Street (elev. 10,152 feet), is in the low 90s.

After completing the 2008 race, Joe Kulak, who lives in Oreland, Pennsylvania (elev. 259 feet), registered an 80. Friends helped him over to the oxygen tanks, where he sucked on the facemask for an hour.

In extreme cases, high-altitude pulmonary edema (swelling or fluid accumulation in the lungs) or cerebral edema (fluid in the brain—a malady which may prove fatal) may occur. Fortunately, these circumstances are rare, and nobody has ever died during the race.

Still, high altitude scares away even the most ambitious runners—especially those living at low elevations. But with the proper approach, even runners from New York City or the Bay Area can excel in rarified air—and enjoy the experience.